The light generated by a laser is usually very directional and propagates for considerable distances with a concentrated light beam intensity. To protect personnel and material from the hazard posed by this concentrated radiation, an appropriate light shield is required. The light shield, if it is used for eye wear or in the optical path of optical instruments, should not prevent radiation, which is outside the spectral emission band of the laser, from being transmitted.
Also, the light shield should not substantially color distort or attenuate the view of the outside world as seen by the observer from a position behind the shield.
Because the eye is the structure most sensitive to damage from laser radiation, the standards of hazard protection based on safe levels for the eye can also be applied to the rest of the human body and to most optical instrumentation. Whether the laser beam would enter the eye directly or indirectly by way of reflection, the eye must be protected by proper attenuation of the laser intensity.
In accordance with the invention, a holographic optical notch filter (reflection grating) which is an analog of a mirror may be used to provide such protection. These filters have narrow bandwidths, reflecting wavelengths in the notch and passing all other frequencies. Depending on the notch, the range of frequency that is reflected will shift as the angle of incidence of the incident light changes. The notch must therefore be widened as the range of angles of incidence widens in order to consistently reflect a particular wavelength. Otherwise, a beam entering at a particular angle of incidence would not be reflected, whereas a beam entering normal to the filter would be reflected.